Impaired Mitochondrial Microbicidal Responses in Chronic Obstructive Pulmonary Disease Macrophages

Endo-phenotyping of COPD patients

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is a heterogeneous syndrome and may comprise several different phenotypes that are driven by different molecular mechanisms (endotypes). Several different clinical, genetic, and inflammatory phenotypes of COPD have been recognized and this may lead to more precise effective therapies.

AREAS COVERED

The different clinical phenotypes, including smoking versus nonsmoking COPD, small airway disease versus emphysema, non-exacerbators versus frequent exacerbators are discussed. Rare genetic endotypes (alpha₁-antitrypsin deficiency, telomerase polymorphisms), and inflammatory phenotypes (eosinophilic versus neutrophilic) are also recognized in stable and exacerbating patients and have implications for the choice of therapy.

EXPERT OPINION

Clinical phenotypes have so far not proved to be very useful in selecting more personalized therapy for COPD. Even with genetic endotypes, this has not led to improved therapy. More promising is the recognition that COPD patients who have increased sputum or blood eosinophils tend to have more frequent exacerbations and inhaled corticosteroids are more effective in preventing exacerbation. Increased blood eosinophils have proved to be a useful biomarker now used to target ICS more effectively. Furthermore, COPD patients with low eosinophils are more likely to get pneumonia with ICS and to have lower airway bacterial colonization.

Macrophages-the immune effector guardians of the lung: impact of corticosteroids on their functional responses

Lung macrophages (LMs) are key immune effector cells that protect the lung from inhaled particulate matter, noxious gases and pathogens. In Chronic Obstructive Pulmonary Disease (COPD), there is an abundance of macrophages in airspaces and lung tissues suggesting that they play an important role in the pathogenesis of the disease. Furthermore, macrophage phenotype and functional properties are altered in COPD toward a more pro-inflammatory state, characterized by reduced pathogen recognition and processing ability and dysfunctional tissue repair qualities. Inhaled corticosteroids (ICSs), used in the management of COPD, has been shown to reduce acute exacerbations of COPD but is also associated with increased occurrence of pneumonia. Corticosteroids treatment altered LM phenotypic characteristics and their functional properties, and this commentary discusses current knowledge and also the gaps in our understanding of the impact of ICS on LMs phenotype and function. A better understanding of how ICSs impact the immune-inflammatory responses in the lung, in particular ICSs’ effects on LMs, could allow more selective personalized tailoring of the use of ICSs in COPD to improve disease progression, morbidity and mortality.

Inhibition of Fatty Acid Oxidation Promotes Macrophage Control of Mycobacterium tuberculosis

Macrophage activation involves metabolic reprogramming to support antimicrobial cellular functions. How these metabolic shifts influence the outcome of infection by intracellular pathogens remains incompletely understood. Mycobacterium tuberculosis (Mtb) modulates host metabolic pathways and utilizes host nutrients, including cholesterol and fatty acids, to survive within macrophages. We found that intracellular growth of Mtb depends on host fatty acid catabolism: when host fatty acid β-oxidation (FAO) was blocked chemically with trimetazidine, a compound in clinical use, or genetically by deletion of the mitochondrial fatty acid transporter carnitine palmitoyltransferase 2 (CPT2), Mtb failed to grow in macrophages, and its growth was attenuated in mice. Mechanistic studies support a model in which inhibition of FAO generates mitochondrial reactive oxygen species, which enhance macrophage NADPH oxidase and xenophagy activity to better control Mtb infection. Thus, FAO inhibition promotes key antimicrobial functions of macrophages and overcomes immune evasion mechanisms of Mtb.IMPORTANCEMycobacterium tuberculosis (Mtb) is the leading infectious disease killer worldwide. We discovered that intracellular Mtb fails to grow in macrophages in which fatty acid β-oxidation (FAO) is blocked. Macrophages treated with FAO inhibitors rapidly generate a burst of mitochondria-derived reactive oxygen species, which promotes NADPH oxidase recruitment and autophagy to limit the growth of Mtb. Furthermore, we demonstrate the ability of trimetazidine to reduce pathogen burden in mice infected with Mtb. These studies will add to the knowledge of how host metabolism modulates Mtb infection outcomes.

Developing Novel Host-Based Therapies Targeting Microbicidal Responses in Macrophages and Neutrophils to Combat Bacterial Antimicrobial Resistance

Antimicrobial therapy has provided the main component of chemotherapy against bacterial pathogens. The effectiveness of this strategy has, however, been increasingly challenged by the emergence of antimicrobial resistance which now threatens the sustained utility of this approach. Humans and animals are constantly exposed to bacteria and have developed effective strategies to control pathogens involving innate and adaptive immune responses. Impaired pathogen handling by the innate immune system is a key determinant of susceptibility to bacterial infection. However, the essential components of this response, specifically those which are amenable to re-calibration to improve host defense, remain elusive despite extensive research. We provide a mini-review focusing on therapeutic targeting of microbicidal responses in macrophages and neutrophils to de-stress reliance on antimicrobial therapy. We highlight pre-clinical and clinical data pointing toward potential targets and therapies. We suggest that developing focused host-directed therapeutic strategies to enhance "pauci-inflammatory" microbial killing in myeloid phagocytes that maximizes pathogen clearance while minimizing the harmful consequences of the inflammatory response merits particular attention. We also suggest the importance of One Health approaches in developing host-based approaches through model development and comparative medicine in informing our understanding of how to deliver this strategy.

Pneumonia recovery reprograms the alveolar macrophage pool

Community-acquired pneumonia is a widespread disease with significant morbidity and mortality. Alveolar macrophages are tissue-resident lung cells that play a crucial role in innate immunity against bacteria that cause pneumonia. We hypothesized that alveolar macrophages display adaptive characteristics after resolution of bacterial pneumonia. We studied mice 1 to 6 months after self-limiting lung infections with Streptococcus pneumoniae, the most common cause of bacterial pneumonia. Alveolar macrophages, but not other myeloid cells, recovered from the lung showed long-term modifications of their surface marker phenotype. The remodeling of alveolar macrophages was (a) long-lasting (still observed 6 months after infection), (b) regionally localized (observed only in the affected lobe after lobar pneumonia), and (c) associated with macrophage-dependent enhanced protection against another pneumococcal serotype. Metabolomic and transcriptomic profiling revealed that alveolar macrophages of mice that recovered from pneumonia had new baseline activities and altered responses to infection that better resembled those of adult humans. The enhanced lung protection after mild and self-limiting bacterial respiratory infections includes a profound remodeling of the alveolar macrophage pool that is long-lasting; compartmentalized; and manifest across surface receptors, metabolites, and both resting and stimulated transcriptomes.

Alveolar Macrophage Apoptosis-associated Bacterial Killing Helps Prevent Murine Pneumonia

Rationale: Antimicrobial resistance challenges therapy of pneumonia. Enhancing macrophage microbicidal responses would combat this problem but is limited by our understanding of how alveolar macrophages (AMs) kill bacteria. Objectives: To define the role and mechanism of AM apoptosis-associated bacterial killing in the lung. Methods: We generated a unique CD68.hMcl-1 transgenic mouse with macrophage-specific overexpression of the human antiapoptotic Mcl-1 protein, a factor upregulated in AMs from patients at increased risk of community-acquired pneumonia, to address the requirement for apoptosis-associated killing. Measurements and Main Results: Wild-type and transgenic macrophages demonstrated comparable ingestion and initial phagolysosomal killing of bacteria. Continued ingestion (for ≥12 h) overwhelmed initial killing, and a second, late-phase microbicidal response killed viable bacteria in wild-type macrophages, but this response was blunted in CD68.hMcl-1 transgenic macrophages. The late phase of bacterial killing required both caspase-induced generation of mitochondrial reactive oxygen species and nitric oxide, the peak generation of which coincided with the late phase of killing. The CD68.hMcl-1 transgene prevented mitochondrial reactive oxygen species but not nitric oxide generation. Apoptosis-associated killing enhanced pulmonary clearance of Streptococcus pneumoniae and Haemophilus influenzae in wild-type mice but not CD68.hMcl-1 transgenic mice. Bacterial clearance was enhanced in vivo in CD68.hMcl-1 transgenic mice by reconstitution of apoptosis with BH3 mimetics or clodronate-encapsulated liposomes. Apoptosis-associated killing was not activated during Staphylococcus aureus lung infection. Conclusions: Mcl-1 upregulation prevents macrophage apoptosis-associated killing and establishes that apoptosis-associated killing is required to allow AMs to clear ingested bacteria. Engagement of macrophage apoptosis should be investigated as a novel, host-based antimicrobial strategy.

Association of urine mitochondrial DNA with clinical measures of COPD in the SPIROMICS cohort

BACKGROUNDMitochondrial dysfunction, a proposed mechanism of chronic obstructive pulmonary disease (COPD) pathogenesis, is associated with the leakage of mitochondrial DNA (mtDNA), which may be detected extracellularly in various bodily fluids. Despite evidence for the increased prevalence of chronic kidney disease in COPD subjects and for mitochondrial dysfunction in the kidneys of murine COPD models, whether urine mtDNA (u-mtDNA) associates with measures of disease severity in COPD is unknown.METHODSCell-free u-mtDNA, defined as copy number of mitochondrially encoded NADH dehydrogenase-1 (MTND1) gene, was measured by quantitative PCR and normalized to urine creatinine in cell-free urine samples from participants in the Subpopulations and Intermediate Outcome Measures in COPD Study (SPIROMICS) cohort. Urine albumin/creatinine ratios (UACR) were measured in the same samples. Associations between u-mtDNA, UACR, and clinical disease parameters - including FEV1 % predicted, clinical measures of exercise tolerance, respiratory symptom burden, and chest CT measures of lung structure - were examined.RESULTSU-mtDNA and UACR levels were measured in never smokers (n = 64), smokers without airflow obstruction (n = 109), participants with mild/moderate COPD (n = 142), and participants with severe COPD (n = 168). U-mtDNA was associated with increased respiratory symptom burden, especially among smokers without COPD. Significant sex differences in u-mtDNA levels were observed, with females having higher u-mtDNA levels across all study subgroups. U-mtDNA associated with worse spirometry and CT emphysema in males only and with worse respiratory symptoms in females only. Similar associations were not found with UACR.CONCLUSIONU-mtDNA levels may help to identify distinct clinical phenotypes and underlying pathobiological differences in males versus females with COPD.TRIAL REGISTRATIONThis study has been registered at ClinicalTrials.gov ( NCT01969344).FUNDINGUS NIH, National Heart, Lung and Blood Institute, supplemented by contributions made through the Foundation for the NIH and the COPD Foundation from AstraZeneca/MedImmune, Bayer, Bellerophon Therapeutics, Boehringer-Ingelheim Pharmaceuticals Inc., Chiesi Farmaceutici S.p.A., Forest Research Institute Inc., GlaxoSmithKline, Grifols Therapeutics Inc., Ikaria Inc., Novartis Pharmaceuticals Corporation, Nycomed GmbH, ProterixBio, Regeneron Pharmaceuticals Inc., Sanofi, Sunovion, Takeda Pharmaceutical Company, and Theravance Biopharma and Mylan.

Decreased expression of a phagocytic receptor Siglec-1 on alveolar macrophages in chronic obstructive pulmonary disease

Background

Alveolar macrophages are professional phagocytes that remove microbial pathogens inhaled into the lung. The phagocytic ability is compromised in chronic obstructive pulmonary disease (COPD). However, the molecular mechanisms underlying this defect in phagocytosis are not clearly defined.

Materials and methods

Cell suspensions were collected from lung tissues of patients undergoing lung resection. Alveolar macrophages were detected as FSC^hi/ SSC^hi/CD45⁺/CD206⁺ cells in the isolated cell suspension by flow-cytometry. The cell surface expression of plasma membrane-bound phagocytic receptors (Fcγ receptor I (FcγRI), a complement receptor CD11b, macrophage scavenger receptor-1 (MSR-1), CD36 and Siglec-1) was determined on the alveolar macrophages. Correlations between the expression levels of the phagocytic receptors and disease severity were analysed. Phagocytosis of fluorescence-tagged bacteria by human alveolar macrophages was evaluated.

Results

The flow-cytometry analyses revealed that FcγRI, CD11b, MSR-1 and Siglec-1, but not CD36, were expressed on human alveolar macrophages. Among these receptors, Siglec-1 expression was significantly decreased on alveolar macrophages in COPD ex-smokers (n = 11), compared to control never-smokers (n = 11) or control ex-smokers (n = 9). The Siglec-1 expression on alveolar macrophages was significantly correlated with lung function (forced expiratory volume in 1 s) and with the severity of emphysema. Treatment of human alveolar macrophages with an anti-Siglec1 blocking antibody decreased phagocytosis of non-typeable Haemophilus influenzae (NTHi).

Conclusion

Our findings demonstrated reduced expression of Siglec-1 on alveolar macrophages in COPD, which is involved in engulfment of NTHi.

Mitochondria: at the crossroads of regulating lung epithelial cell function in chronic obstructive pulmonary disease

Disturbances in mitochondrial structure and function in lung epithelial cells have been implicated in the pathogenesis of various lung diseases, including chronic obstructive pulmonary disease (COPD). Such disturbances affect not only cellular energy metabolism but also alter a range of indispensable cellular homeostatic functions in which mitochondria are known to be involved. These range from cellular differentiation, cell death pathways, and cellular remodeling to physical barrier function and innate immunity, all of which are known to be impacted by exposure to cigarette smoke and have been linked to COPD pathogenesis. Next to their well-established role as the first physical frontline against external insults, lung epithelial cells are immunologically active. Malfunctioning epithelial cells with defective mitochondria are unable to maintain homeostasis and respond adequately to further stress or injury, which may ultimately shape the phenotype of lung diseases. In this review, we provide a comprehensive overview of the impact of cigarette smoke on the development of mitochondrial dysfunction in the lung epithelium and highlight the consequences for cell function, innate immune responses, epithelial remodeling, and epithelial barrier function in COPD. We also discuss the applicability and potential therapeutic value of recently proposed strategies for the restoration of mitochondrial function in the treatment of COPD.

Role of Metabolic Reprogramming in Pulmonary Innate Immunity and Its Impact on Lung Diseases

Lung innate immunity is the first line of defence against inhaled allergens, pathogens and environmental pollutants. Cellular metabolism plays a key role in innate immunity. Catabolic pathways, including glycolysis and fatty acid oxidation (FAO), are interconnected with biosynthetic and redox pathways. Innate immune cell activation and differentiation trigger extensive metabolic changes that are required to support their function. Pro-inflammatory polarisation of macrophages and activation of dendritic cells, mast cells and neutrophils are associated with increased glycolysis and a shift towards the pentose phosphate pathway and fatty acid synthesis. These changes provide the macromolecules required for proliferation and inflammatory mediator production and reactive oxygen species for anti-microbial effects. Conversely, anti-inflammatory macrophages use primarily FAO and oxidative phosphorylation to ensure efficient energy production and redox balance required for prolonged survival. Deregulation of metabolic reprogramming in lung diseases, such as asthma and chronic obstructive pulmonary disease, may contribute to impaired innate immune cell function. Understanding how innate immune cell metabolism is altered in lung disease may lead to identification of new therapeutic targets. This is important as drugs targeting a number of metabolic pathways are already in clinical development for the treatment of other diseases such as cancer.

Accumulation of damaged mitochondria in alveolar macrophages with reduced OXPHOS related gene expression in IPF

BACKGROUND

Impaired mitochondria homeostasis and function are established hallmarks of aging and increasing evidence suggests a link with lung fibrosis. Mitochondria homeostasis may be also affected in alveolar macrophages (AMs) in idiopathic pulmonary fibrosis (IPF). In this study, we used bronchoalveolar lavage (BAL), a tool for both clinical and research purposes, and a rich source of AMs.

METHODS

BAL samples were examined from 52 patients with IPF and 19 healthy individuals. Measurements of mitochondria reactive oxygen species (mtROS), mitochondria morphology and related gene expression were performed. Additionally, autophagy and mitophagy levels were analysed.

RESULTS

Mitochondria in AMs from IPF patients had prominent morphological defects and impaired transcription paralleled to a significant reduction of mitochondria homeostasis regulators PINK1, PARK2 and NRF1. mtROS, was significantly higher in IPF and associated with reduced expression of mitochondria-encoded oxidative phosphorylation (OXPHOS) genes. Age and decline in lung function correlated with higher mtROS levels. Augmentation of damaged, oxidised mitochondria in IPF AMs however was not coupled to increased macroautophagy and mitophagy, central processes in the maintenance of healthy mitochondria levels.

CONCLUSION

Our results suggest a perturbation of mitochondria homeostasis in alveolar macrophages in IPF.

Defective bacterial phagocytosis is associated with dysfunctional mitochondria in COPD macrophages

Increased reactive oxygen species (ROS) have been implicated in the pathophysiology of chronic obstructive pulmonary disease (COPD). This study examined the effect of exogenous and endogenous oxidative stress on macrophage phagocytosis in patients with COPD.Monocyte-derived macrophages (MDMs) were generated from non-smoker, smoker and COPD subjects, differentiated in either granulocyte macrophage-colony stimulating factor (G-Mφ) or macrophage-colony stimulating factor (M-Mφ). Alveolar macrophages were isolated from lung tissue or bronchoalveolar lavage fluid. Macrophages were incubated in ±200 µM H₂O₂ for 24 h, then exposed to fluorescently labelled Haemophilus influenzae or Streptococcus pneumoniae for 4 h, after which phagocytosis, mitochondrial ROS (mROS) and mitochondrial membrane potential (ΔΨm) were measured.Phagocytosis of bacteria was significantly decreased in both G-Mφ and M-Mφ from COPD patients compared with from non-smoker controls. In non-smokers and smokers, bacterial phagocytosis did not alter mROS or ΔΨm; however, in COPD, phagocytosis increased early mROS and decreased ΔΨm in both G-Mφ and M-Mφ. Exogenous oxidative stress reduced phagocytosis in non-smoker and COPD alveolar macrophages and non-smoker MDMs, associated with reduced mROS production.COPD macrophages show defective phagocytosis, which is associated with altered mitochondrial function and an inability to regulate mROS production. Targeting mitochondrial dysfunction may restore the phagocytic defect in COPD.

Mitochondrial biology in airway pathogenesis and the role of NRF2

A constant improvement in understanding of mitochondrial biology has provided new insights into mitochondrial dysfunction in human disease pathogenesis. Impaired mitochondrial dynamics caused by various stressors are characterized by structural abnormalities and leakage, compromised turnover, and reactive oxygen species overproduction in mitochondria as well as increased mitochondrial DNA mutation frequency, which leads to modified energy production and mitochondria-derived cell signaling. The mitochondrial dysfunction in airway epithelial, smooth muscle, and endothelial cells has been implicated in diseases including chronic obstructive lung diseases and acute lung injury. Increasing evidence indicates that the NRF2-antioxidant response element (ARE) pathway not only enhances redox defense but also facilitates mitochondrial homeostasis and bioenergetics. Identification of functional or potential AREs further supports the role for Nrf2 in mitochondrial dysfunction-associated airway disorders. While clinical reports indicate mixed efficacy, NRF2 agonists acting on respiratory mitochondrial dynamics are potentially beneficial. In lung cancer, growth advantage provided by sustained NRF2 activation is suggested to be through increased cellular antioxidant defense as well as mitochondria reinforcement and metabolic reprogramming to the preferred pathways to meet the increased energy demands of uncontrolled cell proliferation. Further studies are warranted to better understand NRF2 regulation of mitochondrial functions as therapeutic targets in airway disorders.

HIV gp120 in the Lungs of Antiretroviral Therapy-treated Individuals Impairs Alveolar Macrophage Responses to Pneumococci

RATIONALE

People living with HIV are at significantly increased risk of invasive pneumococcal disease, despite long-term antiretroviral therapy (ART). The mechanism explaining this observation remains undefined.

OBJECTIVES

To determine if apoptosis-associated microbicidal mechanisms, required to clear intracellular pneumococci that survive initial phagolysosomal killing, are perturbed.

METHODS

Alveolar macrophages (AM) were obtained by BAL from healthy donors or HIV-1-seropositive donors on long-term ART with undetectable plasma viral load. Monocyte-derived macrophages (MDM) were obtained from healthy donors and infected with HIV-1_BaL or treated with gp120. Macrophages were challenged with opsonized serotype 2 Streptococcus pneumoniae and assessed for apoptosis, bactericidal activity, protein expression, and mitochondrial reactive oxygen species (mROS). AM phenotyping, ultrasensitive HIV-1 RNA quantification, and gp120 measurement were also performed in BAL.

MEASUREMENTS AND MAIN RESULTS

HIV-1_BaL infection impaired apoptosis, induction of mROS, and pneumococcal killing by MDM. Apoptosis-associated pneumococcal killing was also reduced in AM from ART-treated HIV-1-seropositive donors. BAL fluid from these individuals demonstrated persistent lung CD8⁺ T lymphocytosis, and gp120 or HIV-1 RNA was also detected. Despite this, transcriptional activity in AM freshly isolated from people living with HIV was broadly similar to healthy volunteers. Instead, gp120 phenocopied the defect in pneumococcal killing in healthy MDM through post-translational modification of Mcl-1, preventing apoptosis induction, caspase activation, and increased mROS generation. Moreover, gp120 also inhibited mROS-dependent pneumococcal killing in MDM.

CONCLUSIONS

Despite ART, HIV-1, via gp120, drives persisting innate immune defects in AM microbicidal mechanisms, enhancing susceptibility to pneumococcal disease.

Melatonin prevents lung injury by regulating apelin 13 to improve mitochondrial dysfunction

Pulmonary fibrosis is a progressive disease characterized by epithelial cell damage, fibroblast proliferation, excessive extracellular matrix (ECM) deposition, and lung tissue scarring. Melatonin, a hormone produced by the pineal gland, plays an important role in multiple physiological and pathological responses in organisms. However, the function of melatonin in the development of bleomycin-induced pulmonary injury is poorly understood. In the present study, we found that melatonin significantly decreased mortality and restored the function of the alveolar epithelium in bleomycin-treated mice. However, pulmonary function mainly depends on type II alveolar epithelial cells (AECIIs) and is linked to mitochondrial integrity. We also found that melatonin reduced the production of reactive oxygen species (ROS) and prevented apoptosis and senescence in AECIIs. Luzindole, a nonselective melatonin receptor antagonist, blocked the protective action of melatonin. Interestingly, we found that the expression of apelin 13 was significantly downregulated in vitro and in vivo and that this downregulation was reversed by melatonin. Furthermore, ML221, an apelin inhibitor, disrupted the beneficial effects of melatonin on alveolar epithelial cells. Taken together, these results suggest that melatonin alleviates lung injury through regulating apelin 13 to improve mitochondrial dysfunction in the process of bleomycin-induced pulmonary injury.

The hormone melatonin could protect lung cells from the damage associated with respiratory diseases such as pulmonary fibrosis. Several studies have linked such damage with abnormal activity of the mitochondria, with these essential metabolic organelles churning out damaging ‘reactive oxygen species’ (ROS), compounds that induce premature cell aging and death. Melatonin can mitigate ROS production, and researchers led by Haihai Liang at China’s Harbin Medical University have demonstrated that it can prevent injury to airway epithelial cells in a mouse model of lung disease. Melatonin treatment countered much of the damage, resulting in significantly longer survival, and the team identified a target molecule in the mitochondria that may be responsible for this effect. This approach could offer hope for a family of diseases with a poor prognosis and limited treatment options.

Inflammatory endotypes in COPD

Chronic obstructive pulmonary disease (COPD) is a major global health problem that is poorly treated by current therapies as it has proved difficult to treat the underlying inflammation, which is largely corticosteroid-resistant in most patients. Although rare genetic endotypes of COPD have been recognized, despite the clinical heterogeneity of COPD, it has proved difficult to identify distinct inflammatory endotypes. Most patients have increased neutrophils and macrophages in sputum, reflecting the increased secretion of neutrophil and monocyte chemotactic mediators in the lungs. However, some patients also have increased eosinophils in sputum and this may be reflected by increased blood eosinophils. Increased blood and sputum eosinophils are associated with more frequent exacerbations and predict a good response to corticosteroids in reducing and treating acute exacerbations. Eosinophilic COPD may represent an overlap with asthma but the mechanism of eosinophilia is uncertain as, although an increase in sputum IL-5 has been detected, anti-IL-5 therapies are not effective in preventing exacerbations. More research is needed to link inflammatory endotypes to clinical manifestations and outcomes in COPD and in particular to predict response to precision medicines.

Integrative Physiology of Pneumonia

Pneumonia is a type of acute lower respiratory infection that is common and severe. The outcome of lower respiratory infection is determined by the degrees to which immunity is protective and inflammation is damaging. Intercellular and interorgan signaling networks coordinate these actions to fight infection and protect the tissue. Cells residing in the lung initiate and steer these responses, with additional immunity effectors recruited from the bloodstream. Responses of extrapulmonary tissues, including the liver, bone marrow, and others, are essential to resistance and resilience. Responses in the lung and extrapulmonary organs can also be counterproductive and drive acute and chronic comorbidities after respiratory infection. This review discusses cell-specific and organ-specific roles in the integrated physiological response to acute lung infection, and the mechanisms by which intercellular and interorgan signaling contribute to host defense and healthy respiratory physiology or to acute lung injury, chronic pulmonary disease, and adverse extrapulmonary sequelae. Pneumonia should no longer be perceived as simply an acute infection of the lung. Pneumonia susceptibility reflects ongoing and poorly understood chronic conditions, and pneumonia results in diverse and often persistent deleterious consequences for multiple physiological systems.

Oxidative stress and macrophages: driving forces behind exacerbations of asthma and chronic obstructive pulmonary disease?

Oxidative stress is a common feature of obstructive airway diseases like asthma and chronic obstructive pulmonary disease (COPD). Lung macrophages are key innate immune cells that can generate oxidants and are known to display aberrant polarization patterns and defective phagocytic responses in these diseases. Whether these characteristics are linked in one way or another and whether they contribute to the onset and severity of exacerbations in asthma and COPD remain poorly understood. Insight into oxidative stress, macrophages, and their interactions may be important in fully understanding acute worsening of lung disease. This review therefore highlights the current state of the art regarding the role of oxidative stress and macrophages in exacerbations of asthma and COPD. It shows that oxidative stress can attenuate macrophage function, which may result in impaired responses toward exacerbating triggers and may contribute to exaggerated inflammation in the airways.

Flipping the kill switch

Alveolar macrophages display an impairment in delayed bacterial killing in chronic obstructive pulmonary disease (COPD) that may contribute to an increased susceptibility to bacterial infection.

Dysregulated Functions of Lung Macrophage Populations in COPD

Chronic obstructive pulmonary disease (COPD) is a diverse respiratory disease characterised by bronchiolitis, small airway obstruction, and emphysema. Innate immune cells play a pivotal role in the disease's progression, and in particular, lung macrophages exploit their prevalence and strategic localisation to orchestrate immune responses. To date, alveolar and interstitial resident macrophages as well as blood monocytes have been described in the lungs of patients with COPD contributing to disease pathology by changes in their functional repertoire. In this review, we summarise recent evidence from human studies and work with animal models of COPD with regard to altered functions of each of these myeloid cell populations. We primarily focus on the dysregulated capacity of alveolar macrophages to secrete proinflammatory mediators and proteases, induce oxidative stress, engulf microbes and apoptotic cells, and express surface and intracellular markers in patients with COPD. In addition, we discuss the differences in the responses between alveolar macrophages and interstitial macrophages/monocytes in the disease and propose how the field should advance to better understand the implications of lung macrophage functions in COPD.

Cigarette Smoke Exposure Inhibits Bacterial Killing via TFEB-Mediated Autophagy Impairment and Resulting Phagocytosis Defect

INTRODUCTION

Cigarette smoke (CS) exposure is the leading risk factor for COPD-emphysema pathogenesis. A common characteristic of COPD is impaired phagocytosis that causes frequent exacerbations in patients leading to increased morbidity. However, the underlying mechanism is unclear. Hence, we investigated if CS exposure causes autophagy impairment as a mechanism for diminished bacterial clearance via phagocytosis by utilizing murine macrophages (RAW264.7 cells) and Pseudomonas aeruginosa (PA01-GFP) as an experimental model.

METHODS

Briefly, RAW cells were treated with cigarette smoke extract (CSE), chloroquine (autophagy inhibitor), TFEB-shRNA, CFTR(inh)-172, and/or fisetin prior to bacterial infection for functional analysis.

RESULTS

Bacterial clearance of PA01-GFP was significantly impaired while its survival was promoted by CSE (p < 0.01), autophagy inhibition (p < 0.05; p < 0.01), TFEB knockdown (p < 0.01; p < 0.001), and inhibition of CFTR function (p < 0.001; p < 0.01) in comparison to the control group(s) that was significantly recovered by autophagy-inducing antioxidant drug, fisetin, treatment (p < 0.05; p < 0.01; and p < 0.001). Moreover, investigations into other pharmacological properties of fisetin show that it has significant mucolytic and bactericidal activities (p < 0.01; p < 0.001), which warrants further investigation.

CONCLUSIONS

Our data suggests that CS-mediated autophagy impairment as a critical mechanism involved in the resulting phagocytic defect, as well as the therapeutic potential of autophagy-inducing drugs in restoring is CS-impaired phagocytosis.

Mitochondrial dysfunction and damage associated molecular patterns (DAMPs) in chronic inflammatory diseases

Inflammation represents a comprehensive host response to external stimuli for the purpose of eliminating the offending agent, minimizing injury to host tissues and fostering repair of damaged tissues back to homeostatic levels. In normal physiologic context, inflammatory response culminates with the resolution of infection and tissue damage response. However, in a pathologic context, persistent or inappropriately regulated inflammation occurs that can lead to chronic inflammatory diseases. Recent scientific advances have integrated the role of innate immune response to be an important arm of the inflammatory process. Accordingly, the dysregulation of innate immunity has been increasingly recognized as a driving force of chronic inflammatory diseases. Mitochondria have recently emerged as organelles which govern fundamental cellular functions including cell proliferation or differentiation, cell death, metabolism and cellular signaling that are important in innate immunity and inflammation-mediated diseases. As a natural consequence, mitochondrial dysfunction has been highlighted in a myriad of chronic inflammatory diseases. Moreover, the similarities between mitochondrial and bacterial constituents highlight the intrinsic links in the innate immune mechanisms that control chronic inflammation in diseases where mitochondrial damage associated molecular patterns (DAMPs) have been involved. Here in this review, the role of mitochondria in innate immune responses is discussed and how it pertains to the mitochondrial dysfunction or DAMPs seen in chronic inflammatory diseases is reviewed.